This invention relates generally to a translational mount for large optical elements, and, more particularly to a translational mount for mirrors utilized in high energy lasers wherein horizontal and vertical translation of the mirror is accomplished by means of rotation of two eccentric rotating rings.
In high energy lasers, it is often necessary to move very large, heavy mirrors to the left, right, up or down in order to align the center of the mirror with the center of the laser beam path (called the optical axis). Examples of the kinds of laser mirrors that require such two-axis translation can be found in a paper by T. R. Ferguson et al, "Conical Element Nomenclatur Use, and Metrology," Optical Engineering, Vol. 21 No. 6 Nov/Dec 1982, pp 959-962. In such laser applications the movement of the mirror must be very small, on the order of a few ten thousandths of an inch, and must be made very smoothly. Heretofore, the positioning of such large optical elements as mirrors in the horizontal and vertical directions orthogonal to its optical axis with the accuracy required for high energy laser applications is accomplished by combining two linear translation stages to produce the desired translations. Such commerically avaiable devices that perform large mirror alignment (such devices are commonly referred to as translation stages) are often too large and bulky to fit into the confined spaces dictated by laser design. Also, since these translation stages are based on sliding mechanisms, a form of friction called "sticktion" limits the smoothness with which they can align heavy mirrors.
More specifically, there are four inherent disadvantages with the utilization of conventional large optic translation mounts for use in high energy laser design. First of all, conventional mounts such as the AEROTECH SMART I CNC positioning table now in use are extremely large and bulky. They require clearances several times greater than the mirror alone would require, and they require clearance in all three dimensions. Since in most high energy laser applications, the components thereof are packed very tightly, conventional translation mounts are difficult to fit therein.
Secondly, the conventional mounts use the linear motion of sliding surfaces to achieve translation. For lightweight mirrors or lenses, such translational movement is perfectly adequate, but for the heavier optics as required in high energy laser systems this type of sliding mount creates the sticking friction which makes it increasingly difficult to achieve the smooth, fine motion that is required to position the optic (mirror or lens) to within the extremely small tolerances required.
Third, conventional mounts create a problem with coupling between two axes of motion. That is, if two separate translation mechanisms are required, one for the horizontal axis and one for the vertical axis they are generally not at right angles to each other. Therefore, motion along one axis will also produce some degree of motion along the other axis. This coupling between axes limits how accurately the mirror can be positioned and places very strict requirements on how the two translation stages must be attached.
The final design disadvantage of the prior art mounting arrangements include the amount of translation force which must be applied to the mirror or optical element. With conventional translation mounts, the optical element must be attached to the face of the mount. Consequently, the optical element (mirror) must be lifted by a force applied some distance from the mirror's center of gravity. This would be analogous to a person lifting a box with arms extended. The effect of such a configuration, for heavy mirrors, is an increase of vibration and friction associated with the sliding mechanisms of the past. Therefore, such arrangements substantially decrease the accuracy to which the mirror position can be held.
It therefore becomes abundantly clear that a need exists for an improved translational mount. In particular, such a translational mount must be capable of supporting large optical elements such as laser mirrors for translational movement in two directions.